Connection-oriented protocols have conventionally been used for switching packets from a source node to a destination node in packet switching networks. Such protocols have found acceptance in the mobile arena with network hardware installed in trucks and other vehicles or hand-carried. Connections between switches in such environments are often short-lived as equipment is moved together or apart, and are of widely fluctuating throughput quality. The challenge of routing data packets in this environment is substantially greater than that of stationary systems. Connection-oriented designs for such systems have been favored because of the need to support telephony as well as machine-to-machine communications. However, IP has become the protocol of choice for end users of such systems, so the need to route IP packets across mobile, ad hoc switching networks has been met by adding IP routers on top of the connection-oriented switches, and developing protocols for establishing the optimal path from one router to another.
The algorithms used by routers to convey connectivity in a mobile network have evolved to keep up with the constantly changing topology, and, as the IP addresses themselves will not convey any topological information when a router can move about freely, they typically use flooding techniques (sometimes called ‘Shortest Path First’ algorithms) to pass local connectivity information on to more distantly-connected routers. A router then uses this information when sending or forwarding packets to another router to decide which way to send the packet. Typically a router will determine which of its nearest neighbors is ‘closest’ to the destination, and then forwards the packet one hop to the chosen neighbor. To do so when the router is attached to a connection-oriented switch, as is the case here, the router must select a virtual circuit on which to place the packet. To facilitate this, it is the current practice for each switch to automatically set up a permanent one-hop circuit to each of its immediate neighbors, with the neighbor forwarding all packets arriving on this circuit to its connected IP router.
When workstations on LANs are attached to a network switch, it is the current practice for whatever device is used to bridge between the LAN and the switch (technically a gateway) to employ the same technique of forwarding all packets addressed ‘off LAN’ to the same one-hop circuit to be forwarded to the IP-router, where the knowledge of the current network topology resides.
The use of multi-hop circuits for faster IP packet transport has faced a number of substantial obstacles: Portable equipment lags the stationary world in terms of size and speed, and mobile switch equipment usually has sufficient memory only for small Virtual Circuit (VC) tables. Hence, circuits have to be used selectively. The paths between switches are in constant flux in a fast moving mobile environment (as, for example, in military or fire-fighting environments), so connections are constantly being broken and re-established. IP is not connection-oriented, so setting up connections as packets arrive for some new destination has proved infeasible since the standard protocols for negotiating a virtual circuit across multiple hops take substantially longer than TCP timeouts tolerate. Knowledge of breaks in connectivity is known first to the switches closest to the break, so packets forwarded by more distant routers will often arrive with the expectation of a (now-broken) path to the destination, and the receiving router must be able to acquire control of the packet, rather than have its connected switch forward the packet further down a no-longer-complete virtual circuit.
For traffic between workstations on different LANs attached by gateways to different switches (in trucks, etc.), the problem is even more difficult since the gateway device bridging between the LAN and a router/switch has no knowledge of the network topology. Nevertheless, fast communications is a must between workstations in ad hoc networks, and there is a real need for better use of the capabilities of the underlying connection-oriented switching network for these communications.
Therefore, there exists a need for a system and method that can implement multi-hop virtual circuit paths in a mobile, ad hoc, connection-oriented packet switching network to support fast and reliable connectivity of connected LANs.